Fix migrations upgrade path for MySQL

For some reason, the migration path from unmanaged db (from alembic
point-of-view) to managed db, through the initial migration works well with
sqlite… But not with mysql where the db system tries to re-create the existing
tables.

This commit is a way to detect if we are migrating from pre-alembic era and
skip the first migration (which would do nothing anyway), marking it as already
executed.

It's quite hackish but that's the best I found so far to get it working with
both MySQL and SQLite.

budget/run.py

@@ -3,7 +3,7 @@ import warnings
 
 from flask import Flask, g, request, session
 from flask.ext.babel import Babel
-from flask.ext.migrate import Migrate, upgrade
+from flask.ext.migrate import Migrate, upgrade, stamp
 from raven.contrib.flask import Sentry
 
 from web import main, db, mail
@@ -15,6 +15,15 @@ from utils import minimal_round
 app = Flask(__name__)
 
 
+def pre_alembic_db():
+    """ Checks if we are migrating from a pre-alembic ihatemoney
+    """
+    con = db.engine.connect()
+    tables_exist = db.engine.dialect.has_table(con, 'project')
+    alembic_setup = db.engine.dialect.has_table(con, 'alembic_version')
+    return tables_exist and not alembic_setup
+
+
 def configure():
     """ A way to (re)configure the app, specially reset the settings
     """
@@ -49,6 +58,11 @@ db.app = app
 # db migrations
 migrate = Migrate(app, db)
 
+if pre_alembic_db():
+    with app.app_context():
+        # fake the first migration
+        stamp(revision='b9a10d5d63ce')
+
 # auto-execute migrations on runtime
 with app.app_context():
     upgrade()